I love Bill's videos and my daughters would tell people that Bill was their pitching coach if anyone asked. I spent a lot of time learning from his video series which I'd highly recommend. But I digress.
Just a couple observations.
In my opinion, bullet spin is due to a late release especially...
I've had decent luck teaching a better close by asking them to finish with the drive knee next to the other [not behind it]. This may be a little exaggerated in practice but seems to work just about right when they are in a game.